McKitterick's doctoral thesis was entitled The Carolingian Renaissance. A Study in the Education of a Society. It was submitted under McKitterick's maiden name of Pierce. The thesis was approved on 24 February 1976.[4] McKitterick's supervisor was Prof. Walter Ullmann.[5]

In 1971 she returned to Cambridge University to pursue her career. She was a Fellow of Newnham College, Cambridge and then became a professorial fellow of Sidney Sussex College. McKitterick has been described as a 'doyenne in her field; her decades of tireless research and teaching have been poured into a steady stream of major publications on Carolingian subjects.'[6] Thomas F. X. Noble considers McKitterick to be 'one of the most original and productive historians of Europe's early Middle Ages'.[7] She has supervised forty-two PhD theses to completion, as of October 2015, with five more in progress.[5] She currently sits on the Council for the British School in Rome.[8]

McKitterick was a Balsdon Fellow at the British School in Rome, April-June 2002. Her research focus was 'Charlemagne in Italy'.[9] From 2005 to 2006 she was a Fellow at the Netherlands Institute of Advanced Study.[10]

In 2018 McKitterick was honoured with an edited volume, Writing the Early Medieval West, to mark her retirement in September 2016. The volume consists of contributions from fifteen of McKitterick's former students.[5]